This invention generally relates to parabolic, dish-shaped antennas for receiving television and other communication signals from relay satellites which are in orbit around the earth.
For domestic television, telephone and other communication uses, the U.S. Government and other organizations have placed a series of relay satellites in a circular geosynchronous orbit about the equator of the earth at a distance of about 22,300 miles as shown schematically in FIG. 1. These satellites receive signals from one place in the United States and relay the signals back to earth so that receptors or antennas at other positions in the United States can pick up the relayed signals. To receive a usable signal from the satellites, the receiver or antenna should be oriented within about 1.degree. of the satellite.
If the signal receptor or antenna is to be located at the equator, the apparent orbit and the actual orbit of the satellites are the same, i.e., circular. However, as the location of the receptor or antenna is moved farther away from the equator the more the apparent orbit of the relay satellites as viewed from the antenna site become oval in shape, which makes the tracking thereof for optimum signal reception very difficult.
To properly receive the signal, the mounting generally used with parabolic dish-shaped antennas is similar in certain respects to the equatorial mount frequently used for telescopes. The base of the parabolic dish is supported on a rotating shaft which is on a polar axis parallel to the earth's axis. In the northern hemisphere the polar axis of the mount is inclined in a true north direction at an angle with the horizontal equivalent to the latitude of the site and the axis of the parabolic dish is pointed generally in the direction of true south with the axis of the dish 90.degree. from the polar axis. To compensate for the change in the shape of the apparent satellite orbit the farther north or south of the equator the antenna site is located, the angle between the support base of the dish antenna and the polar axis must be inclined to the polar axis a gradually increasing amount the farther north or south the antenna site is located. This angle, called the declination or offset angle has been determined for each latitude and it is set forth in the table below.
______________________________________ ANGLE OF OFFSET OR DECLINATION Offset Offset Offset Offset Lat. Angle Lat. Angle Lat. Angle Lat. Angle ______________________________________ 1 .01 16 2.8 31 5.1 46 7.0 2 .36 17 3.0 32 5.3 47 7.1 3 .54 18 3.1 33 5.4 48 7.2 4 .72 19 3.3 34 5.5 49 7.3 5 .90 20 3.5 35 5.7 50 7.4 6 1.07 21 3.6 36 5.8 51 7.5 7 1.25 22 3.8 37 6.0 52 7.6 8 1.43 23 4.0 38 6.1 53 7.7 9 1.60 24 4.1 39 6.2 54 7.8 10 1.78 25 4.3 40 6.3 55 6.8 11 1.95 26 4.4 41 6.5 56 7.9 12 2.13 27 4.6 42 6.6 57 8.0 13 2.3 28 4.7 43 6.7 58 8.0 14 2.5 29 4.8 44 6.8 59 8.1 15 2.6 30 5.0 45 6.9 60 8.2 ______________________________________
This slight modification to the mount allows the position of the antenna dish to be adjusted to receive an optimum signal from one satellite which will then provide optimum reception from essentially all of the satellites within the range of the antenna.
However, these positional requirements make the installation of parabolic dish-shaped antennas by anyone other than highly trained personnel most difficult. The antenna dish can range in size from 6 to 20 feet in diameter which makes the manual control of the unit during the installation and orientation thereof most difficult, particularly with the accuracy required to obtain an optimum signal from the satellites.
Many commercial establishments such as hotels, bars and entertainment centers are installing antennas in order to be able to offer a wider fare of television entertainment to their customers. Moreover, many individuals are also installing these types of antennas for essentially the same reason. However, as more antennas are installed, the need for a more simple method of installation and orientation becomes apparent.
The present invention provides an improved mounting device which greatly simplifies the installation and particularly the orientation of a parabolic dish-shaped antenna.